Why are IRS differentials so expensive

[garyr78]

Getting some quotes on IRS 8.8 differentials for my new MKIV and was floored by the cost for them. They all are in the $1500+ range. Is it possible to get a good quality used one these days?

[2bking]

The raw parts for an aluminum pumpkin, bearings, seals, bolts, and gears run about $700 if you build it yourself. The carrier can be $300 to $600 depending on type (tru-loc, torsen). Except for the $425 pumpkin, these are the same parts that are used in an 8.8 solid axle. You might be able to get a complete T Bird IRS for $300 and rebuild the differential for $300. If you are needing the knuckles and hubs, they would be part of the T Bird IRS.

[tirod]

I appreciate that some would want to rebuild - but - if there is no detectable looseness, a new set of clutch plates for the limited slip is about all that is really needed, some seals, done. That would likely run less than $600.

"New" is nice, these cars rarely run more than 5,000 miles a year, and the power to weight ratio gives the 3,200 pound design intent a strength advantage in a 2,400 pound car. With the power levels typical, the tires break loose and a used diff doesn't see that much abuse - compared to being used in a four wheel rockcrawler with reduction gear box and 40" tires. It usually puts up with that treatment pretty well. Same diff in a different application.

Finishing the car is generally better done sooner than later, a few years from now if you have the differential fail it will be down for a week, vs. adding months to a build completion date because of expenses vs cash flow. Just clean it up and paint it, add synthetic fluid, and get er done.

[Olli]

Actually, you are better off putting a nice fresh IRS diff in. And once you get it in you will understand. You will not want to do it a second time. It really isn't easy to get it in to a stripped chassis let alone a finished car. Most likely a real pain to take it out. It is NOT the same as a re and re of an 8.8 solid rear.

Olli

[jackboeker83]

I pulled an old pumkin out of a Thunderbird at the local pick and pull for 50 bucks. I completely rebuilt it and had it powdercoated and your number is about right because I paid someone to do it for me. If you didnt want to rebuild one I would deff go to the pick and pull place near you and pull one yourself.

[bansheekev]

I got an aluminum case from a wrecked 98 Lincoln MKVIII for $50 and used only the case and rear cover. New Tru-Track differential along with all new gearset, seals, bearings, and flange from Ford Racing. Had a local rear end shop assemble it for me and I was in for $950.

Kevin

[garyr78]

Thanks for the feedback. My MKIV won't be here until late April so I've some time to collect the IRS parts. Thanks.

[Benji]

I wonder if the new Mustang with IRS is going to help bring the cost down of IRS pumpkins, hopefully being mass produced Ford will be able offer it on FRPP for cheaper.

[aspbite]

I wonder if the new Mustang with IRS is going to help bring the cost down of IRS pumpkins, hopefully being mass produced Ford will be able offer it on FRPP for cheaper.

Even if that was the case, unless FFR changes their design it will most likely not fit easily. Completely different animal than the older IRS.

[tirod]

Agreed the IRS is in a tight location.

I just installed a 4EAT AWD Subaru transaxle in my DD and had to get it on the jack after it was under the car. A ratchet strap lifted it up off the floor and the tailshaft was lifted high enough to slide a trans jack under it. I had the teenage son and his buddy do it, but a small floor jack was at hand. If you have a max 45 pound lift capability and arrange your work with a "one man job" perspective then having to armstrong a diff into the chassis becomes an exercise in ingenuity, not brute strength.

If you plan to destroy a used unit, new is NOT stronger unless you know you bought special hi performance aftermarket bearings and parts. New doesn't guarantee anything - used already saw some torque and is a known unit that won't fail. It didn't. New won't guarantee a builder any performance increase - these days it might actually increase the risk of failure unless you absolutely know the source of every part. The used one is at least all OEM, assembled by an technician in a process that does not allow failure, and has that assurance. While some are quite competent in mechanics, the average kit builder isn't a trained professional gifted in adjusting bearings and backlash. Suggesting it's easy and not mentioning all the special tools involved is disengenuous.

Kit builders should tackle what they can accomplish with the skills they have, the want ads are full of half done kits that exceeded their capabilities. I'm not going to be counted as someone who set the bar too high for others to miss. A finished car that gets sorted out is a far better goal than one sitting in the garage waiting for more expensive parts that can only guarantee a few pennies on the dollar improvement in performance.

There are a lot more posts about newly built motors failing than used differentials. It's a different perspective.

[bansheekev]

To Tirod's point I figured how much abuse could a Lincoln MKVIII put in the case. Pretty much none. It was an open differential with something like 273 gears. I viewed it as a leather couch on wheels. $50 for the case was a bargain.

Kevin

[MPTech]

I bought everything I needed from the FFCars Sale forum from fellow members.
Bought an aluminum Lincoln Mark VIII case for $100 and had my friend blast and PC it.
Bought a Ford Trac-Loc diff from another individual.
Then bought a brand-new set of FRP 3.55 Ring&Pinion gears and all new Timkin bearings from someone else.
Took all of my parts to a local shop and they assembled it for me and installed new clutch pads.
I spent less than $1k and I'm really happy with the IRS!

If you can't find something, post a "Wanted" ad.

btw, I also bought a set of Fortes IRS aluminum mounts. This is highly recommended to prevent damage to the mounting points.

[garyr78]

Has anyone recently purchased a IRS pumpkin from Forte? In my forum search for more info about IRS parts I've come across Forte quoting $1200 for them in 2012, now it's $1595, pretty steep inflation in 2 years (33%).

Any recommendations on the brand limited slip internals to buy if I go the rebuild route like so many of you are recommending?

[2FAST4U]

Has anyone recently purchased a IRS pumpkin from Forte? In my forum search for more info about IRS parts I've come across Forte quoting $1200 for them in 2012, now it's $1595, pretty steep inflation in 2 years (33%).

Any recommendations on the brand limited slip internals to buy if I go the rebuild route like so many of you are recommending?

I have an aluminum IRS from Mike. Gorgeous

https://fbcdn-sphotos-f-a.akamaihd.net/hphotos-ak-frc3/t1/389202_2541748232908_1120360897_n.jpg

[Kpt112]

Does anyone know if Mike Forte's package comes with everything you need or just the pumpkin? I am in the process of looking for parts for my IRS as well.

[PaulProe]

I have decided not to pursue a 2nd build so have all the "Ford" pieces of an IRS that I am going to list for sale. Knuckles, hubs, half-shafts(Pin Drive), Alum. Diff. Housing & Ford TrakLok.

email or PM me if you want to discuss. Haven't determined a price yet

Paul

[Kpt112]

Paul,


I am very interested in purchasing your IRS parts. Can you describe the condition and send me a price you are asking for them?

Thanks Kevin


I have decided not to pursue a 2nd build so have all the "Ford" pieces of an IRS that I am going to list for sale. Knuckles, hubs, half-shafts(Pin Drive), Alum. Diff. Housing & Ford TrakLok.

email or PM me if you want to discuss. Haven't determined a price yet

Paul

[pkwest]

It is important to know that if you get a aluminum pumpkin and rebuild it, you must use a case spreader to install the preload shims. I just had one built for my mustang racecar. I put in a t2r, new ford racing 3:55's and a ford racing bearing kit. I had a friend who owns a machine shop do it for me. Im sure he is sorry he offered to do it. He had to build a holder to work on it and case spreader to install the shims. Also keep in mind a center section from a 1999 - 2001 cobra will work. I has posi and the diff is 28 spline. You can use a 03/04 cobra center section which has carbon fiber clutches and is 31 spline but you will need the inner cv joints from a 03/04 cobra also.

[edwardb]

Agreed the IRS is in a tight location.

I just installed a 4EAT AWD Subaru transaxle in my DD and had to get it on the jack after it was under the car. A ratchet strap lifted it up off the floor and the tailshaft was lifted high enough to slide a trans jack under it. I had the teenage son and his buddy do it, but a small floor jack was at hand. If you have a max 45 pound lift capability and arrange your work with a "one man job" perspective then having to armstrong a diff into the chassis becomes an exercise in ingenuity, not brute strength.

If you plan to destroy a used unit, new is NOT stronger unless you know you bought special hi performance aftermarket bearings and parts. New doesn't guarantee anything - used already saw some torque and is a known unit that won't fail. It didn't. New won't guarantee a builder any performance increase - these days it might actually increase the risk of failure unless you absolutely know the source of every part. The used one is at least all OEM, assembled by an technician in a process that does not allow failure, and has that assurance. While some are quite competent in mechanics, the average kit builder isn't a trained professional gifted in adjusting bearings and backlash. Suggesting it's easy and not mentioning all the special tools involved is disengenuous.

Kit builders should tackle what they can accomplish with the skills they have, the want ads are full of half done kits that exceeded their capabilities. I'm not going to be counted as someone who set the bar too high for others to miss. A finished car that gets sorted out is a far better goal than one sitting in the garage waiting for more expensive parts that can only guarantee a few pennies on the dollar improvement in performance.

There are a lot more posts about newly built motors failing than used differentials. It's a different perspective.

Welcome back. You haven't been posting for awhile. :rolleyes: Fact check for the record: I don't know how many forums you read, but this one and the FFCars forum actually quite rarely have partially finished kits for sale. To say the classifieds here are full of them is just not true and offensive on several fronts. While I personally think that FFR may oversell the ease of building these kits just a bit (well at least the time required), it's a testament to FFR (and to the buyer/builders) that so many are completed. And when partially completed kits do get posted, not only are they usually snapped up very quickly, typically the reason is personal. Death in the family, divorce, job change/loss, relocation, financial, other priorities, etc. I've purchased two partially built kits. One about 50% done, the other barely started. Both were sold for personal reasons. Nothing to do with the capability of the builder. There is no data, at least from these forum classifieds, that support your statement.